<!DOCTYPE html>
<html lang="zh">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="renderer" content="webkit" />
  <meta name="force-rendering" content="webkit" />
  <title>CSS 动画背景</title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    body {
      font-family: 'Exo', sans-serif;
    }

    .context {
      width: 100%;
      position: absolute;
      top: 50vh;
      left: 50%;
      transform: translateX(-50%);
      text-align: center;
      color: #fff;
    }

    .context h1 {
      font-size: 35px;
    }

    .area {
      background: #4e54c8;
      background: -webkit-linear-gradient(to left, #8f94fb, #4e54c8);
      background: linear-gradient(to left, #8f94fb, #4e54c8);
      width: 100%;
      height: 100vh;
      position: relative;
      overflow: hidden;
    }

    .circles {
      position: absolute;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      list-style: none;
      padding: 0;
      margin: 0;
    }

    .circles li {
      position: absolute;
      display: block;
      list-style: none;
      background: rgba(255, 255, 255, 0.2);
      animation: animate 25s linear infinite;
      bottom: -150px;
    }

    .circles li:nth-child(1) { left: 25%; width: 80px; height: 80px; animation-delay: 0s; }
    .circles li:nth-child(2) { left: 10%; width: 20px; height: 20px; animation-delay: 2s; animation-duration: 12s; }
    .circles li:nth-child(3) { left: 70%; width: 20px; height: 20px; animation-delay: 4s; }
    .circles li:nth-child(4) { left: 40%; width: 60px; height: 60px; animation-delay: 0s; animation-duration: 18s; }
    .circles li:nth-child(5) { left: 65%; width: 20px; height: 20px; animation-delay: 0s; }
    .circles li:nth-child(6) { left: 75%; width: 110px; height: 110px; animation-delay: 3s; }
    .circles li:nth-child(7) { left: 35%; width: 150px; height: 150px; animation-delay: 7s; }
    .circles li:nth-child(8) { left: 50%; width: 25px; height: 25px; animation-delay: 15s; animation-duration: 45s; }
    .circles li:nth-child(9) { left: 20%; width: 15px; height: 15px; animation-delay: 2s; animation-duration: 35s; }
    .circles li:nth-child(10) { left: 85%; width: 150px; height: 150px; animation-delay: 0s; animation-duration: 11s; }

    @keyframes animate {
      0% {
        transform: translateY(0) rotate(0deg);
        opacity: 1;
        border-radius: 0;
      }
      100% {
        transform: translateY(-1000px) rotate(720deg);
        opacity: 0;
        border-radius: 50%;
      }
    }
  </style>
</head>
<body>
  <div class="context">
    <h1>CSS 动画背景</h1>
  </div>
  <div class="area">
    <ul class="circles">
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
    </ul>
  </div>
</body>
</html>
